How are you?
How are you getting along these days?
It's a long time since I got your last letter.
I‘m glad to have received your letter of Apr.9th.
Give my best regards(wishes) to your mother.
Wish you a pleasant journey.
Wish you the best of health.
Looking forward to your next visit to China.
Looking forward to the pleasure of meeting you.
Expecting to hear from you as soon as possible.
I am looking forward to your reply/hearing from you soon
I look forward to a favorable reply at your earliest convenience.
Your prompt attention to my inquiry would be highly appreciated.
I want to congratulate you with all my heart. I warmly congratulate you on what you’ve achieved.
I am most grateful to you for your help.I want to thank you heartily for what you have done.
Is there any chance of your coming to have dinner with us at our home? We are wondering if you could come to have dinner with us at our home.
I’m delighted to accept your invitation. Thanks for your invitation. I’m certainly looking forward to joiningyou. I haven’t heard from you for ages. How are you doing?